For power combiners that combine a plurality of microwave powers, it is desired that powers are inputted thereto in the same phase to be able to be combined. Moreover, branch ports of such power combiners are desired to have a high isolation property from each other so as to prevent interference between circuits connected to the branch ports, respectively.
As power combiners using striplines, there exists a Wilkinson power distributor. With the Wilkinson power distributor, although it has in-phase distribution and high isolation properties, it has low power durability, causing a problem that it cannot be used with a large power.
As power combiner/distributors using waveguides, a MAGIC-T model has often been used. However, because the MAGIC-T model has a three dimensional shape, it has a complicated structure, causing difficulties in reducing in cost and size and securing the isolation between output ports.
Further, power combining and distribution can be performed by using the conventional waveguide directional couplers. However, when a signal is inputted from a first input port to be distributed to first and second output ports P2 and P3, a relative phase difference between the distributed output signals is 90°; therefore, when the signals are to be used in a combining circuit, a shaft length of a waveguide for the first output port P2 is required to be set longer by ¼ of a guide wavelength than that of a waveguide for the second output port P3 so as to correct 90° of the phase difference. Therefore, a distribution phase variance is caused by influence of frequency properties of the wavelengths of the waveguides, causing a difficulty in obtaining satisfactory distribution properties over a wide band.
JP2592476B discloses a waveguide hybrid coupler. FIG. 17A is a cross-sectional view of a hybrid coupler 10 disclosed in JP2592476B, and FIG. 17B is a cross-sectional plan view taken along a line B-B in FIG. 17A. The hybrid coupler 10 is formed with a first waveguide 12 and a second waveguide 14. Each waveguide has a rectangular cross-section part of which a ratio between the longer wall and the shorter wall is 2:1. The hybrid coupler 10 has two functions: a hybrid coupling function and a phase correcting function for the electromagnetic energy between the two waveguides 12 and 14. A coupling gate 24 arranged in a common side wall 22 has a fixed length substantially the same as a wavelength of one free space of the electromagnetic energy in a longitudinal axis of either one of the waveguides 12 and 14.
Moreover, by arranging the coupling gate 24 in the common side wall of the two waveguides 12 and 14, a hybrid coupler with short slots formed orthogonal to the side wall is configured. A microwave signal coupling between the two waveguides via the gate 24 receives a phase shift by 90° of lag.
Thus, a necessary phase correction is performed by using a set of four capacitive irises 36 arranged in the first waveguide 12 on the side of a penetration port 26 from the gate 24 and a set of four inductive irises 38 arranged in the second waveguide 14 on the side of a coupling port 28 from the gate 24. The capacitive irises 36 in the waveguide 12 configure a phase shifter 40 for causing a phase shift by 45° of lag at the penetration port 26. The inductive irises 38 in the waveguide 14 configure a phase shifter 42 for causing a phase shift by 45° of lead at the coupling port 28. The phase of the signal shifted by 45° through the phase shifter 42 and then by −90° through the gate 24 matches with the phase of the signal shifted by −45° through the phase shifter 40.
The waveguide hybrid coupler disclosed in JP2592476B has a structure in which the plurality of capacitive irises are provided in one of the waveguides to project from its wider face and the plurality of inductive irises are provided in the other waveguide to project from its narrower face. Thus, the entire structure of the unit is complicated, and it has been difficult to fabricate the unit.